1. Field of the Invention
The present invention relates to a semiconductor device and a method of producing the semiconductor device. In particular, the present invention relates to an electrode structure of a semiconductor device formed as a nonvolatile memory, and to a structure for preventing an operation of intentionally reading out the internal data and a method for its production.
2. Description of the Related Art
In recent years, IC cards and, particularly, IC tags mounting a semiconductor device formed as a nonvolatile memory have been widely produced and used. In such semiconductor devices, part of the internal data is written as specific data in such a manner that data cannot be written and read out, and data are suitably written into a writable memory portion.
A nonvolatile memory IC for an IC tag includes antenna pads and a testing pad. FIG. 10 illustrates a conventional nonvolatile memory IC for an IC tag. The IC includes antenna pads 2 and a testing pad 3, formed on a substrate 1, and Au stud bumps 4 are formed on the antenna pads 2. The testing pad 3 is exposed for testing (for writing data). Reference numeral 5 denotes an inorganic insulating film and 6 denotes an organic insulating film.
In the above IC, a test is conducted after the antenna pads 2 and the testing pad 3 are formed, by bringing a testing probe into contact with the antenna pads 2 and with the testing pads 3. A needle scar 7 is formed on the antenna pads 2 and the testing pads 3 at portions where the probe comes into contact.
In the IC tags, the internal specific data, in most cases, must be kept secret and may be a history of the products and personal data. If the internal specific data can be read out or can be rewritten, it is possible that the data can be incorrectly used, which is not desirable.
For example, Japanese Unexamined Patent Publication (Kokai) No. 2003-142539 (pp. 4-6, FIG. 3) discloses a semiconductor device and a method of testing a semiconductor device. According to this testing method, a probe is brought onto a desired terminal without problem even if the surface of the substrate is rough to some extent. As illustrated in FIG. 10, therefore, the data can be read out by bringing the probe into contact with the testing pad 3 even when there is a protrusion such as a stud bump 4 on the surface of the substrate and a difference in height between the stud bump 4 and the testing pad 3. Therefore, the internal specific data may be incorrectly used.
Further, the Au stud bump 4 is expensive to fabricate, and it is desired to fabricate the bumps at a low cost. It is therefore desired to employ a method, of forming the bumps, relying upon electrolytic plating or non-electrolytic plating.
Also, in the fabrication process, the bump is formed on the antenna pad after the steps in which the data are written and the probe is brought in contact with the testing pad. When the bump is formed by electrolytic plating, a seed layer for UBM plating (UBM; under bump metal or under barrier metal) is formed and, then, a metal is plated thereon to form a bump on the antenna pad. If the seed layer (UBM; under bump metal or under barrier metal) is formed on the pads 2 and 3 where the needle scars 7 of the probe remain in a protruded manner, then, the protruded portions of the pads are not covered with the underlying layer to a sufficient degree. Namely, the plated bump metal and the pad metal come into direct contact with each other, a diffusion reaction takes place during use, and the bump strength becomes drops.
Also, in the method of forming bumps relying on the non-electrolytic Ni plating, hydrogen, which is produced during the non-electrolytic Ni plating, penetrates a passivation film and enters into the ferroelectric layer and it becomes probable that the pinning phenomenon occurs to make it difficult to rewrite the data.